This invention pertains to an electrolytic capacitor containing an electrolyte of a metatungstate salt dissolved in a polar solvent. More particularly it pertains to a low-voltage capacitor that retains at least 70% capacity at -40.degree. C.
Low voltage (0-35 V) capacitors generally find use at -40.degree. C. to 85.degree. C. It is desirable that they retain at least 70% capacity at -40.degree. C. Because of the -40.degree. C. operating requirement, water can not be used as a sole solvent. Some water must be present, however, for the reformation of oxide during operation as water is generally the source of oxygen for this reformation.
Ethylene glycol has been used with water to form mixtures that will not freeze, e.g., automotive antifreeze. Other polar organic solvents will also form such mixtures. In addition to this, it is desirable that the solvent system permits adequate conduction of the solute ions, particularly at low temperatures, and this generally requires a relatively low solvent viscosity at low temperatures.